On 7/1/06, Kevin Spinar <spinarkm@gmail.com> wrote:
Is there interest in a clone_ptr class to supplement the current smart_ptr library? A clone_ptr is a smart pointer which performs a deep copy of
pointed-to object whenever the clone_ptr is copied. Also, the
Emailed privately by Pavel Vozenilek: the polymorphic
type is maintained, eg:
clone_ptr<Base> p(new Derived); clone_ptr<Base> p2; p2 = p; /* p and p2 now point to different Derived objects */
What is use case for such behaviour?
The boost.ptr_container library probably does address most of the possible use cases for clone_ptr. In fact, a ptr_container containing only one object could be used instead of a clone_ptr. However, a "container of one object" would be confusing in production code. Maybe clone_ptr wouldn't be used enough to warrant including it in Boost. Perhaps Matt Calabrese, since he showed such enthusiasm, could provide a real-life usage for clone_ptr.
A clone_on_write_ptr is something recognisable but why to clone on copy? This should be addressed.
To me it seems clone-on-copy vs clone-on-write is an optimization issue and not a semantics issue. Considering it isn't possible to determine if someone is merely accessing the object instead of modifying it (foo = *myptr; and *myptr = foo; both use the same operator* and the same operator-> is used regardless whether the member function is const) I don't believe clone-on-write would significantly reduce the number of copies that are made. On 7/2/06, Matt Calabrese <rivorus@gmail.com> wrote:
As a suggestion, if you weren't going to do so already, use the pointer containers' clonable concept to get the cloning functionality required for copies (
http://boost.org/libs/ptr_container/doc/reference.html#the-clonable-concept ).
Yes, that is something I'll look into.